Refrigeration systems typically have a condenser and a receiver downstream from the condenser as separate components. Also, these systems frequently include a subcooler as a separate component downstream from the receiver, but in heat exchange relation with a condenser. A receiver is employed to provide for storage of a volume of refrigerant sufficient to accommodate for variations in system operating conditions and loss of refrigerant. When a system is not in operation, most of the refrigerant is contained in the receiver. Ideally, the refrigeration system will have only the amount of refrigerant in it to accommodate its various operating conditions. This ideal amount can be calculated, and installers of refrigeration systems are advised to charge the system with only that quantity of refrigerant. However, a typical receiver has capacity for storing considerably more refrigerant than what is needed and installers often charge systems with much more than what is needed simply to be certain that there is enough. However, over-charging is undesirable. Also, over-charging, of course, in effect wastes refrigerant and adds to the cost of the system. With inexpensive refrigerants, this may not have been a very significant factor; however, because of environmental concerns, it is now required that different refrigerants are to be employed, and they are more expensive.
The quantity of refrigerant required is also affected by the construction of a conventional receiver. Basically the receiver comprises a container in which liquid refrigerant collects. An outlet tube for withdrawing liquid from the receiver typically extends through an upper wall of the receiver and has an open lower end positioned in the liquid. In order to withdraw only liquid from the receiver, it is necessary that the open lower end be always covered by liquid. Hence, it is necessary that there always be sufficient liquid in the receiver to cover the mouth of the tube. That quantity is essentially an unproductive percentage of the refrigerant from the cooling standpoint.
Another type of receiver simply has an outlet in the lower portion of the container. That type may require smaller minimum amount in the container, but it is undesirable to let the liquid level fall too close to the outlet because there is a vortex effect or tendency for vapor to be drawn into the outlet when the outlet gets close to being uncovered by liquid.
U.S. Pat. No. 4,972,683 discloses an automotive refrigerant condenser that instead of having a separate receiver and a separate subcooler, incorporates those components into a condenser. The particular construction employed, however, is not consistent with that normally used in commercial refrigeration systems. Also, there is no provision in that system to indicate how much refrigerant is to be employed. Presumably, the calculation method would be utilized.
U.S. Pat. No. 5,379,833 discloses a condenser and a subcooler as an integrated unit, with a large capacity receiver between the two also functioning as a vertical header for the condenser. The refrigerant charging procedure is not discussed, but apparently the receiver is large enough to hold all the refrigerant.
Another approach for determining when adequate refrigerant has been injected into a system is to employ sight glasses through which an installer can observe bubbling through the sight glasses which indicates vapor and liquid flowing through the conduit, or observe no bubbling which indicates that only liquid is flowing through the conduit. U.S. Pat. No. 3,753,356 discloses several systems employing sight glasses. It mentions that in one prior system a receiver has been equipped with numerous sight glasses or valve taps at various levels, or with a single vertical sight glass, connected to the vessel at two levels, to determine the level of liquid refrigerant. As an improvement, that patent suggests having a flow-through sight glass at the inlet to a receiver and a second sight glass at the outlet from the receiver. The patent indicates that if there are no bubbles through the sight glass at the outlet there is adequate refrigerant in the system. Further, if no bubbling is seen through the sight glass at the inlet to the receiver, the user knows that there is too much refrigerant in the system. A difficulty with this arrangement is that the difference between just enough refrigerant and too much is equal to a large percentage of the receiver volume. That is, even if the receiver is almost full of refrigerant, bubbles could still be observed through the sight glass at the inlet to the receiver. Yet the system would have much more refrigerant than desired.
Another arrangement illustrated in U.S. Pat. No. 3,753,356 does not include a receiver and has refrigerant flowing directly from the condenser to a subcooling coil, with a sight glass between those two components and with a second sight glass at the outlet of the subcooler. The patent indicates that bubbling in the sight glass at the outlet of the condenser with no bubbling at the outlet of the subcoil would be an indication that the proper amount of refrigerant is in the system. However, bubbles in the subcooler are undesirable in order to maximize the subcooling effect.
It is believed that a need exists for an improved condenser construction and method that will maximize the condenser capacity while minimizing the refrigerant required. Also needed is a simplified technique for determining when there is enough refrigerant in the system.